A 14.5" upper is just a "part" and can be ordered directly through Bushmaster and shipped to your house.
HOWEVER: if you have an AR lower that is not a registered machine gun or short barrel rifle, you can be arrested for constructive possession of an unreg. SBR if caught.
If you have a preban lower, you order or have a gunsmith [Joe's in New Briatin] permanently attach a longer flash hider to it to make the 16" legal limit, if you have a post ban lower, order one without the bayo lug and with a permanently attached muzzle brake.
Or just register it and wait, but the post/pre laws still apply in CT regardless of a fed registration.